In the present study the intrinsic nerve plexuses of the basal cerebral arteries, derived from aged non-Alzheimer's and aged Alzheimer's disease patients were quantified and compared. A previous study described and quantified nerve density on similar arteries from healthy middle-aged patients. Whole-mount preparations of various segments of the basal cerebral arteries were stained for protein gene product 9.5. The deep nerve plexuses, located at the adventitial-medial border, were quantified by image analysis. Transverse cryostat sections were stained for various markers and quantified. Measurements on whole mounts demonstrated that nerve densities were highest in the posterior communicating artery and in the postcommunicating part of the posterior cerebral artery (PCA) for both aged and Alzheimer's groups. Statistical comparison showed a tendency toward decreased nerve density with aging, which was significant for the internal carotid artery, precommunicating part of the PCA, and the anterior choroidal artery in both non-Alzheimer's and Alzheimer's aged groups. In addition, in Alzheimer's patients nerve density was significantly lower in the precommunicating part of the anterior cerebral artery compared with the healthy aged group. Measurements on sections confirmed the tendency to decreased innervation with aging. It is concluded that densities of deep perivascular nerves of human basal cerebral arteries are subject to localized changes caused by aging and Alzheimer's disease.